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The survival strategies of microphytobenthos : behaviour and physiology


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Jordan, Leonie Jane 2009 , 'The survival strategies of microphytobenthos : behaviour and physiology', Research Master thesis, University of Tasmania.

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Microphytobenthos (MPB) need photoadaptive strategies to survive the highly
dynamic light environment in which they reside. They are able to adjust their
photosynthetic activity by physiological regulation or behaviourally by migrating
vertically through the sediment. This study investigates the effects of the time of day on
the vertical migration of benthic diatoms at two sites near Hobart, Tasmania using a pulse
amplitude modulation fluorometer (Water PAM; Walz, Effeltrich) to measure chlorophyll
fluorescence. Chlorophyll a content and maximum quantum yield (Fv/Fm) were used to
examine the profiles of microalgal biomass and photosynthetic properties within
sediment cores, both diurnally and over a 12 month experimental period. The results
show a seasonal pattern of chlorophyll a biofilm development, with maximum values
attained in summer at Pipe Clay Lagoon and in spring at Browns River. A greater amount
of biomass was observed in the muddier sediment at Browns River with a sharper peak of
chlorophyll a compared to the gradual incline then decline at Pipe Clay Lagoon. Fv/Fm
values changed throughout the day with the cells more quenched at midday than sunrise
while experiencing the highest illumination.
Xanthophylls can provide photoprotection to MPB cells by cycling between
epoxide and de-epoxide forms to dissipate excess light energy as heat. The second part of
the study examined the xanthophyll cycle in microphytobenthos on tidally exposed
sediment at Browns River. The goal of this work was to examine whether
microphytobenthos at Browns River used the xanthophyll cycle as a physiological
defence against photoinhibition during a natural light-dark cycle (day-night). A High
Pressure Liquid Chromatography (HPLC) system was used as a pigment separation
technique followed by pigment detection using a photodiode array and quantification
against pure pigment standards. A pulse amplitude modulated (PAM) fluorometer was
used to determine the chlorophyll fluorescence and assess photosynthetic performance in
terms of maximum PSII quantum yield (Fv/F,,,), non-photochemical quenching and Ek in
the field. Changes in PAM fluorescence and xanthophyll: chlorophyll a ratios suggests
that MPB were under physiological stress at noon. The results indicate that the MPB cells
exposed to light at the surface migrated deeper into the •sediments to replenish the epoxide form of their xanthophylls. Overall the result suggests that MPBs utilise both
behavioural and physiological strategies to survive in the dynamic intertidal environment.
This research highlights the importance of the photoadaptive strategies of MPB in
a changing light environment with particular reference to the need for more than one
strategy. This research on MPB ecology helps to form a more accurate picture on survival
strategies while it underlines the fact that previous research has shown inconsistencies.
Further research is needed in this area, particularly in the southern hemisphere, to lessen
these inconsistencies and build on current knowledge.

Item Type: Thesis - Research Master
Authors/Creators:Jordan, Leonie Jane
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Available for use in the Library and copying in accordance with the Copyright Act 1968, as amended. Thesis (MSc)--University of Tasmania, 2009. Includes bibliographical references

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